Software "free" data processing GIS and Remote Sensing

Some software for data processing GIS (geographic information system) and remote sensing can be operated in "free" without having to buy a license. Its capabilities are equivalent to other software that is licensed. Below are some software that can try to operate in GIS data processing.
Quantum GIS
GIS software ArcGIS looks somewhat similar to this can be downloaded at: http://www.qgis.org/.
In the link are also available from the help of the manual and the QGIS blog forum for all users who want to discuss and share information.

GRASS
This is the software for data processing of remote sensing imagery (remote sensing). Can be downloaded at: http://grass.osgeo.org/download/index.php, and to the manuals can be downloaded at the link: http://www.grassbook.org/, sometimes by opening the link download QGIS, GRASS This is installed with atomatis. Please try to unlock features basic image processing. Personal opinion, I was a little difficult at first to open the (ordinary), but could try to further advance the software on this one.
ILWIS
ILWIS GIS is a data processing software as well as remote sensing with the principles of raster based. Developed initially by the ITC (www.itc.nl), and now the software is already in the category of open source. Can be downloaded at: http://www.ilwis.org/. ILWIS facilities include several remote sensing image processing (RGB, composite band, Principle Component), if the digital data DEM (Digital Elevation Model), making anaglyph (3D view of the image of DEM with optical image), hydro processing facility drainage pattern maker (the river flow) of the DEM data, and others.
RAT
RAT is a "mouse" symbol of open source software for radar imagery. Can be downloaded at: http://radartools.berlios.de/. Image processing software applications such as radar and radar image intensity manufacturing (multilook) processing interferometry, polarimetric radar. All can be operated here. For those who like Linux, UNIX or Mac OS X, RAT is very compatible in that OS. Some experiments can also be operated in the window.
NEST
RAT NEST is somewhat similar to that for image processing was developed by the Agency radar.Software Antarika Europe (EOS: European Space Agency http://www.esa.int). This software can process and read the data from the radar platform is already known as: RADARSAT-2, Envisat, ERS-1, ERS-2, Alos PAlsar, TerraSAR. Some level of data can be read here. For more details about what facilities are included in this software can go to this link: http://nest.array.ca/web/nest.